Are SCR's the RHSC of the Rebreather World?

[Windwalker]

I have been interested in rebreathers for a bit. I had the option of going and doing a Drager Dolphin Demo up in Washington a while back and I got to do a couple dives with an SCR. Simple as could be, Crack a valve and go play in the water. I thought that was the coolest thing since the invention of the diving bell. It had Tons of bottom time (with the proper sonic valve) and there was not a lot to worry about (Except sucking spit out of the mouthpiece)

SO I went home and I read up on Rebreathers. But when I was doing my research, I found SCR's and CCR's. Now, everything seems to be either ECCR's or MCCR's with absolutely no mention of SCR's except for a few questions about the Dragers.

Now, My Local dive shop still sells the SCR, but I am noticing most people go OC - SCR - CCR, so I am thinking to myself. WHY? If a SCR will do Rec Depths for 4 hours with little to worry about managing a dilutant or Oxygen Partial pressure.. Why would someone who is doing Rec Diving move from a SCR to a CCR? If the Progression is to move to a CCR, why not just go straight there?

Also my Dive shop who does not sell CCR's, tells me that they are dangerous, twice as expensive to purchase and maintain, and are more complicated. (Ok, I know their agenda.. they want to sell me an SCR)

Forget about the dangerous aspect, that has been beat to death on this board and others.. Twice as expensive (6k vs 8-10k.. Ehh.. Whatever.), but more complicated seems to be true, even for the KISS.

What is the general take, Why is the SCR the Proverbial "Red Headed Step Child" of the Rebreather world?

 

[ScubaDadMiami]

You can kill yourself on either unit if not used properly. Don't be fooled into thinking that SCR doesn't require any extra effort over open circuit diving while CCR requires constant monitoring.

Most SCRs are not built for deeper diving (though they can be rigged to do so, and some can even be converted into full CCR). They are more like gas extenders. They still make bubbles, which takes away from interaction with fish. They also typically offer less bottom time than CCR. Last, SCRs actually call for even longer decompression than on open circuit.

Closed circuit is a constant best mixing machine, and will provide the least amount of decompression obligation of all three: OC, SCR and CCR. It will also provide the longest bottom time for a given amount of gas. It makes no bubbles except when the diver ascends. So, photographers prefer it.

In the end, why purchase equipment that is limited from the start? There really isn't much reason to go SCR these days when you can pay a bit more to go for full CCR.

Yes, it is more complicated. So, if you only dive twice a year and don't want to deal with the extra effort, don't buy one. Stick with open circuit gear in that case.

 

[Windwalker]

Yes, I read the wonderful sticky in this sub forum. Great info. It was looking like to me, no one is bothering with SCR's anymore. The SCR Dragers that I dove had (only) one Oxygen sensor. They did not bubble "All the Time" but I would imagine more frequently then CCR's. I can understand why the gas management and decompression being reduced because you could theoretically use any noble gas as a dilutent and reduce your PP of O or N. Am I correct in assuming that after the inital purchase.. training.. etc that the cost of operation is pretty much the same between an SCR and CCR (assuming they use the same amount and type of scrubber)
If that is the case, then why even bother with an SCR in the first place? Surely there is a Niche where an SCR is more capable then a CCR? Isn't there?

I think that last question is mainly rhetorical, as I think I am sold on a CCR.. I guess, I just have to find an LDS that trains, maintains, and sells them.

Am I correct in the assumption that most of the CCR's have similar max bottom depths? I know I saw number like 100M for the Inspiration, wouldn't the limiting factor be the max depth for the flow control valve and electronics?

Thanks for your responses.

 

[ScubaDadMiami]

Sometimes the depth rating has to do with the gas supply regulator, such as in a KISS style machine, and sometimes it has to do with things like the gas spaces within the handsets. It all depends on which rebreather you are talking about.

 

[wedivebc]

If a SCR will do Rec Depths for 4 hours with little to worry about managing a dilutant or Oxygen Partial pressure..

This comment caught my attention. Unless you are using a big tank like 80cuft you won't get 4 hrs out of a dolphin. You might get 2 hours from a standard dolphin tank but with the 60% orifice you are limited to the MOD of 60% ~ 55ft For deeper dives you need more O2 flow so the tank empties faster. For 100ft dive you can expect 1 hr duration. The other issue is if you change your dive plan and go shallower you still only get 1hr unless you brought a different nitrox mix and change to a smaller flow orfice.
Bottom line the SCR has very little benefit over OC with some increased risk. Since you are interested in RBs I would say go CCR or you could do what I did. Buy a dolphin, close the loop and make your own CCR by converting a very well made SCR.
The dolphin is well constructed and was quite innovative in its day. With lower cost reasonably reliable CCRs hitting the market these days the dolphin has passed its prime.
BTW ther is a guy in your home town who is an expert on the subject of CCR conversions CCR Dolphin

 

[grazie42]

I started asking the same questions you did about a year ago (though I do dive deep on OC and want to continue doing so on RB)...

I´ll take delivery of my MCCR (a rEvo) at the end of this month...What may seem a bit counterintuitive is that CCRs have much better "NDLs" even in the shallow range (60-120ft)...using software I could get about 100mins @ 80ft and still be within the limits of my "CCR OW-course"(agency dependant)...

There certainly are risks (some of which are unit dependant and a lot which are diver dependant) and only you can know if the benefits for your diving outweigh these risks and the cost...

Since you seem to have "researched" you propably already know, but in case you don´t, Rebreather World - Rebreathers for Scuba Diving - the next step is a good place to look for answers...

 

[Meng_Tze]

What is the general take, Why is the SCR the Proverbial "Red Headed Step Child" of the Rebreather world?

Without going into details of differences between CCR and SCR, basically why would you pay a significant amount for a 'gas extender' (SCR) when for the same price (or a little more) you can have a 'permanent gas mixer' (CCR)?

 

[Windwalker]

Thanks for the responses. I have poked around on both this site and rebreather world, however, since I am more "Known" here, I figured I would not be seen as trolling with my question. It seems most you guys cross pollinate over onto that board. I am definatly going to go into a rebreather, right now I am weighing the pro's and con's of a eCCR and a mCCR. But I think ultimately its going to come down to infrastructure and local area support.

 

[Mr.X]

Thanks for the responses. I have poked around on both this site and rebreather world, however, since I am more "Known" here, I figured I would not be seen as trolling with my question. It seems most you guys cross pollinate over onto that board. I am definatly going to go into a rebreather, right now I am weighing the pro's and con's of a eCCR and a mCCR. But I think ultimately its going to come down to infrastructure and local area support.

I have all types of CCRs. In the end, the mechanical one works when the electronics go to the toilet...and they will. It's just a matter of when. The CIS, Meg, Insp. etc. have gone dodgy from time to time over the past decade. The MCCR keeps working, but it has other issues.

X

 

[Windwalker]

I have all types of CCRs. In the end, the mechanical one works when the electronics go to the toilet...and they will. It's just a matter of when. The CIS, Meg, Insp. etc. have gone dodgy from time to time over the past decade. The MCCR keeps working, but it has other issues.

X

What about taking an eCCR and lowering the set point and managing it as a mCCR, I know you have the solenoid as a single point of failure, Are there eCCR's with Selenoid bypasses for underwater mCCR usage?